On second thoughts, start the cart right in the centre of the largest treadmill obtainable. This to avoid a turbulent air rotor at the end of the treadmill affecting the cart.
OK then, time to give Spork a break, he doesn't want to start all over again.
I read jjcote's thought experiment (love thought experiments) he he
forum.hanggliding.org/viewtopic.php?t=8888&postdays=0&postorder=asc&start=60
So the power that can be extracted from a given wind speed is limitless, you just gotta increase the size of the sail. Dead downwind with a symmetrical spinnaker you still stuck in first gear (1:1).
Second gear, which is really a continuously variable gearbox (depending on how much you sheet in) needs a aerodynamic airflow, with suck and suchlike, lets you go any direction at any speed you like, provided that you are cunning enough.
nuff said?
